-O in 6.8.3

Hello,
This is on the recent topic of very eager inlining in ghc-6.8.3.
I wrote recently that
(1) 6.8.3 takes 7 times more of heap than 6.8.2 to complile under -O
a certain small-size module RsePol_ (let us call it M.hs),
(2) even the needed ~70 Mb in 6.8.2 looks unnaturally large.
After thinking a bit, I take back (2).
For `making' M under -Onot -- all right, it must suffice about 20 Mb.
But -O allows deeper optimization, this needs more inlining, inlining
pieces between modules, inlining instances (to some extent).
I expect that -O needs for compilation not more than about 5 times
greater expence in memory and time than -Onot.
ghc-6.8.2 satisfies this.
And 6.8.3 does not, its ratio is about 35 on the example of
RsePol_.hs
What is the developer's idea abot -O/-Onot cost ratio for RAM and
time?
What is the difference between ghc-6.8.2 and ghc-6.8.3 ?
The former does not inline instances under -O and the latter does
inline?
As to the 10-20 % of the result code increase, I am calm about this
-- if something it bought by this. But I am not an expert and do not
see in what point 6.8.3 is better, at least the DoCon performance is
not greater. I do not know, maybe some bugs are fixed, and a bug fix
often costs some code increase, and a bug fix is good.
Regards,
-----------------
Serge Mechveliani
mechvel at botik.ru